A PROSPECTIVE RANDOMIZED CONTROLLED TRIAL USING ROENTGEN STEREOPHOTOGRAMMERTRIC ANALYSIS OF THE ADVANCE MEDICAL PIVOT KNEE: 2 YEAR RESULTS

Abstract

Purpose: The Advance Medial Pivot (MP) knee has higher congruency and postulated different kinematics than traditional posterior stabilized knee implants. This could lead to increased micromotion at the tibial component/bone interface potentially resulting in premature loosening. To investigate the stability of the MP knee we used maximum total point motion (MTPM) as determined with RSA to compare micromotion at the tibial component/bone interface between the Advance MP and PS knees.

Methods: A power calculation determined that a minimum sample size of 40 (20/group) was required. Sixty-six patients (48 females) with primary osteoarthritis of the knee were randomized to receive the Advance MP (n=36) or PS (n=30) knee. Three experienced knee surgeons followed a standardized surgical technique (PCL resection, patella resurfacing, RSA bead placement in polyethylene and tibia) and post-operative protocol (CPM as tolerated, no drains, WBAT). SF-36, WOMAC, PCS, KSCRS were administered to all patients pre-operatively and at 6, 12 and 24 months post-operatively and BMI was recorded. Within 4 days of surgery and at 6, 12 and 24 months post-operatively patients underwent bi-planar x-rays.

Results: Fifteen patients were lost to follow-up (2 infections, 1 death, 2 dropped out, 10 lost due to technical issues). There was no difference in MTPM between groups at 2 years. Physical function was better (p< 0.03) for the PS group at 6 months but there was no difference at 1 year.

Conclusions: There was no difference in MTPM between groups at 2 years post-op. The Advance PS knee appears to result in earlier post-operative improvements in physical function. The altered kinematics and increased congruency of the Advance MP knee does not seem to alter the forces at the tibial component/bone interface and therefore does not appear to be more prone to migration and premature aseptic loosening.

Funding : Other Education Grant

Funding Parties : Unrestricted grant from Wright Medical Inc.